Precise and accurate models of DNAs, RNAs, and polynucleotides are being developed using X-ray fiber diffraction, UV circular dichroism and IR dichroism. The effect of nucleotide composition and sequence on the different secondary structures assumed is being determined. Speculative models of nucleic acids interacting with drugs, repressors, and polymerases are being produced. BIBLIOGRAPHIC REFERENCES: Selsing, E., S. Arnott, and R.L. Ratliff. 1976. The conformations of poly (dA-dT-dT) poly (dA-dA-dT). J. Mol. Biol. 98:243-248. Arnott, S. and E. Selsing. 1975. The conformation of C-DNA. B. Mol. Biol. 98:265-269.